Screw Conveyor Specifications: Diameter, Incline, and Capacity Sizing

A screw conveyor is a simple-looking piece of equipment — a helical screw rotating inside an enclosed trough or tube — but getting the spec right still requires matching several interdependent variables to your actual material. Here's what to check before locking in a design.

U-Trough vs Tubular: The First Configuration Decision

U-trough (open) screw conveyors are the standard, cost-effective configuration — easy to access for cleaning and maintenance, and suited to most free-flowing and moderately cohesive materials.

Tubular (enclosed) screw conveyors provide full containment. They're the better choice for fine powders, dusty materials, or anywhere complete dust-tight operation is a requirement rather than a nice-to-have — food-grade or pharmaceutical lines, and materials where product loss through an open trough is a real cost.

This decision should come before diameter or drive sizing — it changes accessibility for maintenance and affects how the rest of the spec gets built.

Diameter, Incline, and Drive

Screw conveyors are available from 150mm to 500mm diameter as standard (larger available on request), running horizontally or at inclines up to approximately 30°. Beyond that incline, conveying efficiency drops off sharply and a different conveying method (bucket elevator, pneumatic conveying) usually makes more sense.

Drive is via a VFD-controlled gearmotor, which allows fine control of feed rate — useful where the screw conveyor is metering material into a downstream process rather than just transferring it in bulk. Bearing configuration uses end and intermediate hanger bearings; for longer conveyor runs, intermediate bearing spacing and material becomes a real design consideration, not just a structural afterthought, since hanger bearings are also a common wear/failure point in abrasive service.

Capacity Depends on More Than Diameter

Rated capacity for the standard range runs 1–100 t/hr, but where in that range a specific conveyor lands depends on:

• Screw diameter — larger diameter moves more material per revolution
• Pitch — the spacing between flights along the shaft; standard pitch equals diameter, but reduced pitch is used for inclined runs or where more controlled, gentler handling is needed
• Rotational speed — higher RPM increases throughput but also increases wear rate and can degrade fragile materials
• Material bulk density and flowability — the same screw geometry moves very different tonnages of a dense granule versus a light, aerated powder

This is why a "150mm screw conveyor" isn't a complete spec on its own — diameter alone doesn't determine capacity without pitch, speed, and material data attached.

Construction and Wear Options

Standard construction is mild steel or stainless steel SS304/316, selected based on product contact requirements and corrosion exposure. For abrasive materials — minerals, some fertilizers, recycled or filled plastics — ENZAC offers hardened or wear-resistant lined screw conveyors to extend service life between rebuilds. Food-grade stainless construction is available for hygienic applications where product contact surface finish and cleanability matter.

Additional options worth specifying up front rather than retrofitting later: a jacket for heating or cooling (relevant for temperature-sensitive materials like some fats and waxes), and a dust-tight cover for U-trough configurations that need better containment than the open trough alone provides but don't need a full tubular redesign.

What to Send With Your Enquiry

Because so much of a screw conveyor's performance comes down to matching diameter, pitch, incline, and construction material to your actual product — not a generic model number — a proper spec starts with: material bulk density, flowability/Carr Index, required throughput (t/hr), conveying distance and incline angle, and whether the application is dusty, abrasive, temperature-sensitive, or hygienic-grade. Review the full Screw Conveyor specification range before finalising a transfer method for your line.